Cation Effect on the Water Activity of Ternary (S)‑Aminobutanedioic Acid Magnesium Salt Solutions at 298.15 and 310.15 K

Vapor pressure osmometry was applied to the system aminomethanamidine hydrochloride (guanidinium hydrochloride, GndmCl) + (S)-aminobutanedioic acid hemimagnesium salt (magnesium l-aspartate, Mg-(l-Asp)2) + water for varying molalities of GndmCl and Mg-(l-Asp)2 (m Mg‑(Asp)2 = 0.1, 0.2, and 0.3 mol/kg and m GndmCl = 0.1–1.2 mol/kg) at T = 298.15 and 310.15 K. From vapor pressure osmometry, activities of water, activity coefficients of water, and the corresponding osmotic coefficients of the mixtures Mg-(l-Asp)2 + water and Mg-(l-Asp)2 + GndmCl + water have been calculated, both being directly related to the chemical potentials of the different species and therefore to their Gibbs energy. Electrolyte perturbed-chain statistical associating fluid theory (ePC-SAFT) accounting for Coulomb and short-range (hard chain, dispersion, association) interactions was used to model the own experimental data of binary Mg-(l-Asp)2 + water and ternary GndmCl + Mg-(l-Asp)2 + water solutions. ePC-SAFT was further applied to model osmotic coefficients of NaGlu + KCl + water, NaGlu + NaCl + water, NaAsp + NaCl + water, NaAsp + KCl + water, aminoethanoic acid + NaNO3 + water, and aminoethanoic acid + NaSCN + water as well as thermodynamic properties of these solutions such as fugacity coefficients and activity coefficients of the mixture components. Without fitting any parameters to data of the ternary salt + aminoethanoic acid + water system, osmotic coefficients, ϕ, and activity coefficients of water, γ1, and aminoethanoic acid have been predicted, and ϕ and γ1 were in good agreement with the experimental data. In contrast, a negative binary interaction parameter kij had to be introduced to model ϕ of ternary systems salt + amino acid salt + water in accurate agreement with the experimental data.